1. Field of the Invention
The present invention relates to a mold effectively used for producing a multilayer molded article in which skin materials are adhered to a base member made of a thermoplastic resin, and a method for producing a multilayer molded article.
2. Description of the Related Art
A multilayer molded article in which skin materials are adhered to the outer surface of a base member made of a thermoplastic resin is excellent in aspect of production costs, lightweight property and shape-imparting property and is frequently used in a wide range of fields including interior parts (e.g. door trims, instrument panels) of automotive vehicles and interior and exterior parts of household appliances.
Molded objects having a plurality of design surfaces formed on the outer surfaces thereof (hereinafter may also be referred to as “multifaced molded objects”) are known as the above multilayer molded articles. For example, if a plurality design surfaces having different patterns or materials are formed, the outer surfaces of a base member can be effectively decorated. Molded objects in which one skin material having a plurality of design surfaces is adhered to the base member and molded objects in which a plurality of skin materials are adhered to the base member are known as the above multifaced molded objects. A molded object having a plurality of skin materials adhered thereto is produced, for example, by producing a multilayer molded article according to a molding method for supplying a molten resin to the rear surfaces of a skin material and adhering the skin material and the resin (injection molding method, compression molding method, etc.), then by producing a plurality of multilayer molded articles by the same way, and then by joining these multilayer molded articles on the same plane by, e.g. heat sealing (fusing). The multifaced molded object is also produced by producing a resin base member by an injection molding method, a press molding method (compression molding method) or the like, and adhering a plurality of skin materials to the outer surface of the base member. However, joint portions of the base members may lack strength according to the former method, whereas the skin materials may come off according to the latter method.
As a method for solving these problems, a method is known according to which, for example, a mold comprised of a pair of male and female mold parts are used, two skin materials are inserted into the mold parts with the rear surfaces thereof faced toward the male mold part after being adhered adjacent to each other on the same plane, a molten resin is supplied from the male mold part to adhere the skin materials and the resin. FIG. 1 is a schematic top plan view of a multifaced molded object (planned) sought to be produced by the above producing method, FIG. 2 is a schematic sectional view of the multifaced molded object (planned) when viewed from front, FIGS. 3 and 4 are schematic sectional view used for the explanation of the producing method, and FIG. 5 is a top plan view of the multifaced molded object actually produced by the producing method. As shown in FIGS. 1 and 2, the planned (aimed) multifaced molded object is such that two skin materials (first skin material 1, second skin material 2) are adhered adjacent to each other on the outer surface of a base member 4 made of a thermoplastic resin. A boundary portion (boundary line) 3 between the skin materials 1 and 2 forms a straight line. As shown in FIGS. 3 and 4, a joined skin material in which the first and second skin materials 1, 2 are joined at the boundary portion 3 is inserted into a mold comprised of a male mold part 14 and a female mold part 15 in the case of producing the multifaced molded object. The joined skin material is inserted with the rear surfaces thereof faced toward the male mold part 14 and the front surfaces thereof held in contact with the female mold part 15. A first gate 11 for supplying a molten resin to the rear surface of the first skin material 1 and a second gate 12 for supplying a molten resin to the rear surface of the second skin material 2 are formed in a molding surface (mold surface) of the male mold part 14, and the molten resin is supplied from these gates 11, 12 (see FIG. 3). Then, the female mold part 15 is moved toward the male mold part 14 to mold the resin while pressing it (see FIG. 4). However, according to such a method, the resin coming out from one gate (resin 21 coming out from the first gate 11 in this example) may reach the boundary portion (joined portion) 3 earlier than the resin coming out from the other gate (resin 22 coming out from the second gate 12 in this example), resulting in displacement of the boundary portion 3. Thus, as shown in FIG. 5, the boundary portion 3 between the first and second skin material 1 and 2 meanders, making it difficult to form a straight line (planned line).
In view of the above, a method for molding a resin while fixing a boundary portion 3 has been proposed (Japanese Unexamined Patent Publication No. 2-175111). FIGS. 6 and 7 are schematic sectional views used for the explanation of this method. This example differs from the one shown in FIGS. 3 and 4 in that a boundary portion 3 between skin materials 1 and 2 is held by a fixing jig 50 embedded in a male mold part 14 (see FIG. 6). However, even if the boundary portion 3 is fixed, an unfixed portion of the boundary portion 3 may be strongly pushed as shown in FIG. 7 if one resin 21 reaches the boundary portion (joined portion) 3 earlier than the other resin 22, resulting in a large displacement of the boundary portion 3. Therefore, similar to the example shown in FIGS. 3 and 4, the boundary portion 3 may meander in this example as well.
In the above examples, the two skin materials are used. However, even in the case of using one skin material, the position of the boundary portion may be displaced if a plurality of design surfaces is formed on its outer surface.
Regardless of whether two skin materials are used or one skin material is used, arrival timings of the resins at the boundary portion may largely differ if the design surfaces have largely different areas, if the molded object has a complicated projected and recessed shape, or if the number of the gates increased due to the large size of the molded object. Such largely different arrival timings are likely to degrade the appearance of the molded object due to a displacement of the boundary portion and wrinkling near the boundary portion.